Where? Finland specifically, or elsewhere? Both my local tram system in Germany as well as DB as the national infrastructure operator in Germany have construction tolerances of only +/- 2 mm. Maintenance tolerances on the other hand can be quite a bit larger, at least in the plus direction (on the order of 15/20/25 mm).

Sure, but thats Germans. I'm surprised it isn't specc'd in 10ths.

They should've specced 1435mm±410µm, with no broadening at curves.

I just wish the Germans would be as accurate with their train schedules as they are with their rail gauge tolerances :D